1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing a semiconductor device.
2. Related Art
As a method of forming a Fin portion of a Fin transistor, a spacer-lithography technique is proposed. As the spacer-lithography technique, a Sidewall pattern Transfer (SWT) technique is known.
The SWT is a method which can form Fin portions at a pitch smaller than the minimum pitch of lithography. Conventional SWT is executed by the following method. A silicon nitride film is deposited on an SOI (Silicon On Insulator). Furthermore, in a region for forming a Fin, a hard mask such as a TEOS film on poly-Si film is formed on the silicon nitride film. In a region (for example, a pad region of a source-drain electrode for connecting adjacent Fins to each other) except for the Fin region, a photoresist mask is formed on the silicon nitride film. By using the hard mask and the photoresist mask as masks, the silicon nitride films are simultaneously etched by RIE (Reactive Ion Etching). The patterned silicon nitride film is used as a mask when an SOI film under the silicon nitride film is etched. The etched SOI layer is used as a Fin.
In this manner, in the conventional SWT, the silicon nitride film is etched by using both of the hard mask and the photoresist mask as masks. When the silicon nitride film is etched with high anisotropy of RIE, the photoresist mask is etched at a speed higher than the etching speed of the hard mask. More specifically, in this case, selectivity between both the hard mask and the photoresist mask and the silicon nitride film cannot be easily assured.
On the other hand, when etching is performed with low anisotropy of RIE, a sidewall shape of a silicon nitride film etched by using the hard mask may be tapered. More specifically, the verticality of the side wall of the patterned silicon nitride film is deteriorated. In this manner, the width of a Fin formed by using the silicon nitride film as a mask becomes ununiform, or the width becomes larger than a desired width disadvantageously.
Therefore, when both the hard mask and the photoresist mask are used as masks, Fins having a pitch smaller than the minimum pitch of lithography and each having a uniform width cannot be easily formed.